Modern Drilling Equipment for Underground Applications J M Reynolds Atlas Copco Construction and Mining Australia ABSTRACT: Hydraulic drilling rigs are still used today for the same applications as when they were first released around thirty years ago. However, modern control systems allow drilling functions to be much more tightly controlled, which improves the productivity and accuracy of the drilling process. It is now possible for operators to follow a drill pattern displayed on a screen and manoeuvre the drill feeds, which are also represented on the screen, to the correct position of each hole. This allows for the contour of the tunnel to be better controlled than by conventional methods and can reduce over-break and ground support requirements. It is also possible for modern rigs to drill the round automatically. Further to blast hole drilling, the other main application for drilling rigs is in the area of ground support. Telescopic (or split feeds) allow for bolting in low roof heights without sacrificing development round length. It is also possible for these feeds to be utilised for extension drilling of cable bolt holes and probe holes. Installation of canopy tubes utilising the Odex system is an extension to the capabilities of tunneling drill rigs. INTRODUCTION The productivity of underground drilling equipment has increased markedly over the past sixty years. The “Swedish Method” of drilling was introduced in the 1940’s and utilised a pneumatic rockdrill and pusher leg. This combination allowed one man to produce 10 drill metres per hour. In the 1970’s, twin boom hydraulic drill rigs were introduced, allowing one man to produce 125 drill metres per hour. The current generation of three boom drilling rigs allow one man to produce up to 275 drill metres per hour.
ous machines which are available, from single boom rigs for small drifts, to large three boom rigs for big cross sections.
• Single boom rigs – cross sections up to 20m2
Figure 1. The evolution of drilling productivity
RIG TYPES Not all tunnels are the same. Hence, there are a variety of different sized drilling rigs and different feed positioning systems to cater for different tunneling applications. The following diagrams illustrate vari-
More commonly used in narrow vein mining applications, rigs such as the Boomer 104 can be used for small civil projects such as access adits or service tunnels.
• Twin boom rigs – cross sections up to 45m2
• • • •
Rockdrill output power Drilling consumables Operator skill Maintenance practices
The first three points listed above are very much related in that different ground conditions require different drill bit geometries and energy input for efficient rock breakage. For this reason, drill rigs need to be setup specifically for a particular site to account for changes in ground conditions or application from project to project. In order to maximise the productivity and economics of the drilling process, the expertise of OEM’s can be utilised through involvement in setting up of drilling equipment and the selection of appropriate drilling consumables.
• Twin boom rigs – cross sections up to 104m2
• Three boom rigs – cross sections up to 179m2
Operator skill levels will have a significant effect on the productivity of a drill rig. Sufficient training of operator personnel is required to ensure that machines are used safely, effectively and with minimimal damage. This is again an area where the services of OEM’s can add value to a project. With drilling equipment becoming more powerful and with many new features becoming available, the area of maintenance and trouble-shooting has a significant effect on machine productivity. The advent of computer control systems requires site maintenance personnel to have knowledge that extends beyond traditional diesel and hydraulic fitting skills. In-built diagnostic systems have simplified the trouble-shooting process to a certain degree, however it is becoming increasingly common for service personnel to require basic knowledge of computer networks and communication systems. In order to ensure such competence exists on a project site, assistance from equipment suppliers is available to either train customer service personnel or to provide the service function on behalf of the customer. DRILL RIG FUNCTIONS There are two basic functions that tunneling drill rigs perform – blast hole drilling and rock reinforcement. Blast hole drilling
RIG PRODUCTIVITY There are many factors that combine to determine the productivity of a modern hydraulic drill rig, including:
• Ground conditions
Blast hole drilling is no longer just about penetration rate. There is now increasing focus on hole accuracy, which is a function of two things:
• Is the hole in the right direction? • Is the hole in the right spot?
In conjunction with appropriate blasting techniques, hole accuracy has a significant impact on tunnel development, particularly in the area of contour control and associated over-break. Minimising over-break has many benefits, in particular where such overbreak needs to be back-filled with expensive concrete. Waste haulage costs are also minimised if over-break can be controlled.
In the Hong Kong project, two Rocket Boomer WL3C drill rigs work side-by-side on a 110m2 face, each drilling 77 holes and a total of three additional large diameter cut holes. The rigs operate predominantly in “Total” mode, except on contour and lifter holes when protruding rocks get in the way. When this is the case, the machines are operated in “Regular” mode.
The introduction of computer control systems onto drilling rigs has allowed for greater accuracy in both hole direction and location. For example, the ABC “Regular” system available on Atlas Copco tunneling rigs allows drill plans to be loaded into the onboard computer for the operator to follow. The computer screen not only shows the drill pattern, but also displays the actual drill feed location relative to the hole. The operator simply aligns the feed to the hole on the screen and is ready to begin drilling, with the hole in the right spot. Lookout angles are also accounted for in the drill pattern and hole alignment process. The drill rig itself is located in the tunnel relative to a tunnel line laser.
Figure 3. Rocket Boomer WL3C drill rigs
The penetration rate achieved using 48mm spherical button bits is around 2.5m/min, which allows for a face to be drilled out by two rigs in 2-2.5 h. When only one rig is available to drill the round, it takes closer to 4 h. For further information regarding drilling equipment utilised on this project, refer to the Face Drilling technical reference resource book produced by Atlas Copco. Rock reinforcement Figure 2. Drill plan display – ABC “Regular”
The ABC “Regular” system also captures the results of the actual drilled hole locations and direction for comparison with the planned pattern. This can be used for monitoring purposes or to take corrective action if necessary. It is also now possible for a rig to drill out a round in automatic mode, with the operator utilised for observation purposes. This level of automation is called ABC “Total”.
Drill rigs are often used to drill holes for rock bolts and in some cases to install them also. In cases where the tunnel height is low, there may be a tradeoff between the round length and bolt hole length due to space limitations. However, this trade-off can be minimised via the use of telescopic feeds. As the name suggests, the length of these feeds can be changed via the telescoping action of two feed rails mounted on top of each other. The following diagrams illustrates the geometry of the feed and its method of operation.
The ABC “Regular” and ABC “Total” systems have been used on many tunneling projects since their introduction in the late 1990’s. Projects include the Lotschberg rail tunnel in the Swiss Alps, the Skatestraum road tunnel in Norway and the West Rail DB350 rail tunnel contract in Hong Kong. Figure 4. A telescopic drill feed
of the tunnel line to assist in determining conditions ahead. Canopy tubes
Figure 5. Telescopic feeds – method of operation
An example of such a feed is the BMHT6818/10, which allows for a 2.8m hole to be drilled in its nonextended state and a 5.2m hole to be drilled in its extended state. When drilling a 2.8m bolt hole, the feed can fit comfortably in a 5m high excavation and still be able to be extended to drill a 5.2m face round, which is far more productive than a 2.8m face round would be. Conversely, if a standard feed was used and the productivity of a 5.2m face round was preferred, a tunnel height of around 7.5m would be required to allow the feed to drill bolt holes into the roof.
In poor ground conditions, underground drill rigs are commonly used to install arched support structures ahead of the excavation. This is achieved using a modified feed arrangement in conjunction with the Odex method of overburden drilling. As shown in the diagram below the Odex system employs a pilot bit and eccentric reamer to drill a hole large enough to accommodate a casing tube, which is driven in during the drilling process. As shown in figure 7 below, when the end of the hole is reached, the direction of rotation is reversed and the drill string can be retracted, leaving the casing tube behind.
Bolt-hole length restrictions due to space constraints can also be overcome by use of extension drilling. This is a common requirement when cable bolts need to be installed. Extension drilling can take on a number of forms:
• Manual rod adding. A rod gripper arrangement is fitted to the end of the feed to facilitate coupling and un-coupling of rods. Extra rods are added manually.
• Single rod adding. A rod gripper arrangement is complimented with a set of swing arms mounted on the feed which add a second rod to the drill string without manual intervention. The following diagram illustrates the arrangement.
Figure 6. Mechanised rod adding
• Rod adding carousel. A rod magazine is added to the rod gripper and swing-arm arrangement for mechanised rod handling of multiple drill rods. Further to cable-bolt hole drilling, extension drilling is also commonly used for drilling probe holes ahead
Figure 7. The Odex method
Canopy tubes have been used on many projects in Australia, such as the Melbourne Citylink tunnels, the M5 tunnel and the Ryde storm-water tunnel. A European case example is the Mrazovka road tunnel in Prague, where grouted canopy tubes were installed over the tunnel entrance. A canopy consisting of 23 grouted tubes was maintained ahead of excavation, with 12m installation intervals. A 90mm pilot bit and 123mm eccentric bit were used to drill ahead of 115mm perforated tubes. The tubes were threaded and came in 3m lengths to make up the installation depth of 12m. Following installation, the tubes were pressure grouted to form the protective canopy above the excavation space. It can take up to 48 hours for a 12m canopy to be installed and grouted. There was a requirement for a 4m overlap between canopies, so only 8m of advance was possible with each canopy installation.
NEW DEVELOPMENTS
remotely, however a robust communication system with guaranteed bandwidth is necessary.
The introduction of computer control systems has added a new range of capabilities to underground drilling rigs. Boomer tunneling rigs from Atlas Copco can be equipped with options such as Measure While Drilling (MWD), Mine Map Navigation (MMN), Mine Drill Plan Generator (MDPG), Rig Remote Access (RRA), and Single Machine Remote Control (SMRC). The MWD system logs a number of key drilling parameters during drilling of probe holes. Analysis of this data can provide information on ground conditions ahead of the tunnel, allowing for corrective actions to be planned prior to reaching an area where bad conditions are predicted. MMN has been developed primarily for mining applications to eliminate navigation errors underground. The drill rig is located in the mine via reference points and tunnel alignments that are presented on the operators screen.
Figure 9. Mine Drill Plan Generator display
CONCLUSION The productivity of tunneling drill rigs has increased substantially over the years. This increase in productivity, coupled with advances in computer control systems and associated add-on features allows modern drill rigs to carry out an extensive range of functions in both civil and mining applications. REFERENCES Face Drilling, 2nd edition. Atlas Copco Rock Drills AB. Atlas Copco Overburden Drilling – the Odex Method G2. Atlas Copco Craelius AB. Figure 8. Mine Map Navigation display
MDPG is an extension of the capabilities of the ABC “Regular” drill plan display system and MMN. MDPG allows a rig to generate its own drill plan at the face, based on the conditions it meets on arrival and its position within the mine. RRA allows a drill rig to be integrated into the site computer network. With the rig being part of the network, drill plans, data logs and other information can be transmitted to/from the machine via a radio modem, mobile phone or LAN connection. Machine trouble-shooting can even be done from Sweden via the internet. An extension of RRA is Single Machine Remote Control. This option allows a machine to be operated
